West Ham have signed Northern Ireland defender George McCartney from Sunderland - with Clive Clarke heading in the opposite direction.
The total deal is worth £1million to Sunderland - with West Ham paying £600,000 plus Clarke for the 25-year-old left-back.
McCartney will be out for another eight to 10 weeks with a knee injury sustained in a pre-season friendly against Shelbourne in Dublin last month.
But he passed an initial medical at West Ham last night and completed his move to Upton Park today.
McCartney will compete with left-back Paul Konchesky for a first-team place, though he can also offer cover at centre-back.
He is West Ham's sixth new signing of the summer as manager Alan Pardew's prepares for a UEFA Cup campaign, joining defenders John Pantsil, Tyrone Mears and Jonathan Spector plus midfielder Lee Bowyer and striker Carlton Cole.
Clarke, meanwhile, heads for the Stadium of Light after a frustrating season in which he made just three appearances for West Ham.
Sunderland tried unsuccessfully to sign Clarke from Stoke last summer before he completed a £275,000 move to Upton Park.
Clarke had hoped the move to West Ham would further his international career with the Republic of Ireland.
But his opportunities were limited, first by injury and then the consistent form of Konchesky who missed only one league game all season.